This invention relates to packaging of glass substrates (glass sheets) and, in particular, to the dense packing of glass substrates of the type which are subject to high levels of flexing as a result of vibration during transport and a significant gravity sag when held horizontally.
More generally, the invention relates to high density packaging of sheets of any material for which flexing during transport and/or gravity sag when held horizontally is a problem, e.g., sheets having surfaces that can be damaged through contact and/or sheets that are brittle and can break through contact and/or excessive flexing. For ease of presentation, however, the following discussion is in terms of sheets of glass, specifically, sheets of glass for use in manufacturing liquid crystal displays (LCDs), it being understood that the invention as defined in the appended claims is not so limited except for those claims which specify that the material is glass or a liquid crystal display glass.
Large, thin glass sheets are used as substrates for liquid crystal displays. During transport from a glass manufacturing facility to a customer, the substrates are packaged either in an L-shape support or in a polypropylene box, each sheet being separated from its neighbors by having its non-quality edges held in grooves. See U.S. Pat. Nos. 5,588,531 and 5,904,251.
The flexibility of such substrates increases as the size of the sheet increases and/or its thickness decreases. Such an increase in flexibility, in turn, means that the sheets exhibit a higher level of flexing as a result of vibration during transport and a larger gravity sag when held horizontally. As a result, a large spacing between sheets and careful transport are required to avoid glass damage and breakage due to excess flexing (bending) and/or contact between adjacent sheets. Such a large spacing increases the costs of storing, transporting, and handling the substrates.
A need has thus existed for improved techniques for packaging flexible substrates that allow the substrates to be packed closer to each other and to exhibit less horizontal sag than with existing techniques. This need has intensified in recent years and is expected to be even more pressing in the future as glass substrates for LCD applications become larger and thinner, and thus more flexible. The present invention addresses this continuing need in the art.
In view of the foregoing, it is an object of this invention to provide apparatus and methods for overcoming the flexing and sag problems exhibited by large and/or thin substrates. It is an additional object of the invention to provide methods and apparatus for increasing the packaging density of flexible substrates. It is a specific object of the invention to reduce the likelihood of damage to a flexible substrate as a result of vibration during transport and/or sag when held horizontally.
To achieve these and other objects, the invention in accordance with one of its aspects provides a container (19) for holding a plurality of sheets (13) of a flexible material, said sheets being flat in their non-stressed condition, said container comprising a first side (21) and an opposing second side (23), the first side comprising a first plurality of curved grooves (25) and the second side comprising a second plurality of curved grooves (25), wherein the first and second pluralities of curved grooves are aligned with each other so as to form a plurality of pairs of curved grooves, each pair being adapted to receive a sheet of the flexible material, each curved groove of each pair having substantially the same radius of curvature (R), said radius of curvature being selected to apply an elastic strain to the sheet of flexible material to thereby reduce the likelihood of contact between sheets in adjacent pairs of grooves as a result of handling of the container. Preferably, the radius of curvature is greater than two meters and less than five meters, although other radii of curvature can be used in the practice of the invention if desired.
In accordance with another of its aspects, the invention provides a method for increasing the number of sheets of a flexible material that can be transported in a container, said sheets being flat in their non-stressed condition, said method comprising applying an elastic strain to at least one of the sheets while the sheet is in the container to reduce the likelihood of contact between the sheet and an adjacent sheet as a result of handling of the container. Preferably, an elastic strain is applied to each of the sheets in the container and, most preferably, the same elastic strain is applied to all of the sheets.
Additional features and advantages of the invention are set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed.
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.